1. Field of the Invention
The present invention relates to emulsified cosmetics comprising blended therein resin particles which have a spherical, flat, and smooth surface and a uniform particle size, and which create a smooth and uniform spread and an “unsticky” feeling.
2. Description of the Related Art
In general, a cosmetic in which oil phase components such as oils or waxes are emulsified with aqueous phase components using an surfactant (emulsifier) is referred to as an emulsified cosmetic. An emulsified cosmetic has higher durability on a skin surface than does a fine particle cosmetics, provides a moist feel, and has superior dispersibility of fine particles, thus enabling wide-ranged applications including, for example, creams or foundations.
Because a typical emulsified cosmetic is constituted by emulsifying the aqueous phase components with the oil phase components as described above, it is necessary that these components retain a stable emulsification state. Recently, it has become common for spherical resin particles to blended in to improve the tactile feel of the cosmetic. Many of these spherical resin particles are easily uniformly dispersed into the oil phase, but lack an affinity for the aqueous phase, therefore, it is essential to prevent detachment, aggregation, alteration, and the like from occurring. For this problem, it is common to apply methods of blending an emulsion stabilizer, the surfactant, and the like.
A disadvantage of such emulsified cosmetics is their sticky sensation, giving a feeling of thick spread because of poor spreadability during application. Especially when the spreadability during application is poor, an applied cosmetic layer becomes thick or uneven, which is likely to create an unnatural impression. Further, in a recent trend, there has been an increasing desire for cosmetics that provide a natural finish. A natural finish is commonly accomplished by forming a thin and uniform cosmetic-applied layer on the skin. Lately, methods of blending talc powder or spherical polyalkylene resins (Japanese Patent Publication Laid-open No. 11-130617) into the cosmetics are adopted to remove stickiness and improve smooth spread during application.
The spherical resin is typically subjected to surface treatment such as oil solution treatment, silicone compound treatment, fluorine compound treatment, metallic soap treatment, surfactant treatment, amino acid compound treatment or water-soluble polymer treatment, generally in order to add functional characteristics such as water repellency or oil repellency. However, these treatments effect the sensation after application, and not to improving dispersibility. Recent studies have resulted in particles having a strong affinity for the oil phase and aqueous phase because of presence of an organic group bonded directly to part of silicon in silica fine particles and through having a hydroxyl group in part of silicon (Japanese Patent Publication Laid-open No. 2001-151640). However, further improvement in tactile feelings such as an adhesive feeling and smoothness during application, and in reducing the high manufacturing costs of seed polymerization, remain an unfulfilled desire.
According to available studies, the spreadability of cosmetics depends upon physico-chemical properties such as particle shape, particle size distribution, surface conditions, and hardness of these blended spherical particles, and the characteristics of the cosmetics are greatly dependent upon physico-chemical properties such as a glass transition point and average molecular weight, and upon monomers constituting the resin and a weight ratio. Further, cosmetic durability required in the cosmetics is greatly affected by a resin acid value, percentage of moisture content of compounds, water resistance based on the content of impurities and oil resistance.
The conventional spherical particles blended into the emulsified cosmetics were most commonly spherical resin particles prepared by an emulsification polymerization method, a general purpose suspension polymerization method or a precipitation polymerization method, or talc powder. However, because the particle size distribution of the spherical particles prepared using these methods is wide and the surface conditions of the particles are not controlled, there has been a desire for development of cosmetics superior in spreadability of cosmetics when applied and in forming a uniform cosmetic layer.
There has been an especially strong desire for development of emulsified cosmetics in which the spherical resin particles have an affinity not only for the oil phase but also for the aqueous phase, and which demonstrate superior stability.